- Isotope Exchange Reaction of Formate with Molecular Hydrogen on Ni(110) by IRAS
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Kinetics of the CH/CD isotope exchange reaction of formate (HCOO(a)/DCOO(a)) on Ni(110) with gaseous D2/H2 was investigated below the decomposition temperature (360 K) by infrared reflection absorption spectroscopy (IRAS).The apparent activation energies of HCOO(a) -> DCOO (a) and DCOO(a) -> HCOO(a) reactions were derived as 52 +/- 5 and 58 +/- 5 kJ*mol-1, respectively.A half-order dependence of the reaction rate on hydrogen pressure was observed, suggesting that the rate-determining step was the reaction of the adsorbed formate with reversibly adsorbed hydrogen atom The reaction of HCOO(a) with D2 was 2.1 +/- 0.3 times faster than that of DCOO(a) with H2 at 300 K, and the origin of the isotope effect is discussed.
- Yamakata, Akira,Kubota, Jun,Kondo, Junko N.,Domen, Kazunari,Hirose, Chiaki
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- Formation of Glyoxylic Acid in Interstellar Ices: A Key Entry Point for Prebiotic Chemistry
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With nearly 200 molecules detected in interstellar and circumstellar environments, the identification of the biologically relevant α-keto carboxylic acid, glyoxylic acid (HCOCOOH), is still elusive. Herein, the formation of glyoxylic acid via cosmic-ray driven, non-equilibrium chemistry in polar interstellar ices of carbon monoxide (CO) and water (H2O) at 5 K via barrierless recombination of formyl (HCO) and hydroxycarbonyl radicals (HOCO) is reported. In temperature-programmed desorption experiments, the subliming neutral molecules were selectively photoionized and identified based on the ionization energy and distinct mass-to-charge ratios in combination with isotopically labeled experiments exploiting reflectron time-of-flight mass spectrometry. These studies unravel a key reaction path to glyoxylic acid, an organic molecule formed in interstellar ices before subliming in star-forming regions like SgrB2(N), thus providing a critical entry point to prebiotic organic synthesis.
- Eckhardt, André K.,Bergantini, Alexandre,Singh, Santosh K.,Schreiner, Peter R.,Kaiser, Ralf I.
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supporting information
p. 5663 - 5667
(2019/03/29)
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- Reductive transformation of CO2: Fluoride-catalyzed reactions with waste silicon-based reducing agents
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CO2 is one of the most important “renewable” carbon sources. To transform CO2 to useful organic compounds, we examined the reactivity of two model silicon-based “waste” materials, disilanes and metallic Si powder, as reducing agents. In these reactions, fluoride salts were found to be active catalysts: CO2 was converted to formic acid at atmospheric pressure in the presence of H2O as a proton source and the silicon-based reducing reagents. Based on in-situ NMR and kinetics analyses, a hydrosilane and penta-coordinate Si species are proposed as the reaction intermediate and active species, respectively.
- Motokura, Ken,Naijo, Masaki,Yamaguchi, Sho,Miyaji, Akimitsu,Baba, Toshihide
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p. 434 - 439
(2017/04/06)
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- A biomimetic photoelectrocatalyst of Co-porphyrin combined with a g-C3N4 nanosheet based on π-π Supramolecular interaction for high-efficiency CO2 reduction in water medium
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Aiming at high-efficiency biomimetic CO2 photoelectrochemical conversion, a photoelectrocatalyst with excellent CO2 catalytic activity was designed and prepared by immobilizing CoTPP (cobalt meso-tetraphenylporphyrin) onto g-C3N4 conveniently via self-assembly based on π-π supramolecular interaction. The quasi 3-D structure of CoTPP showed a suitable hole with a size of 3.8 ? × 9.6 ? which favoured CO2 adsorption. The pores formed by the π-π stacking of CoTPP and g-C3N4 also provided additional space for CO2 adsorption, which was confirmed by the appearance of a desorption peak at 250 °C in the temperature programmed desorption measurement for CoTPP/g-C3N4. As a normal efficient homogeneous catalyst in organic media, CoTPP commendably maintained outstanding CO2 photoelectrocatalytic activity in heterogeneous aqueous solution, even at a low overpotential of -0.6 V (vs. normal hydrogen electrode, NHE). Under 8 h PEC CO2 reduction, formic acid generation on CoTPP/g-C3N4 reached 154.4 μmol with a TON of 137 and high selectivity of nearly 100% in liquid products. The formation of CoTPP-COO- and CoTPP-COOH intermediates by the Co(ii) active site and CO2 was investigated by in situ UV-vis and Raman spectra. Moreover, an isotopic labelling experiment indicated that water supplied abundant protons for the production of formic acid.
- Liu, Jibo,Shi, Huijie,Shen, Qi,Guo, Chenyan,Zhao, Guohua
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supporting information
p. 5900 - 5910
(2017/12/26)
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- Artificial Z-scheme constructed with a supramolecular metal complex and semiconductor for the photocatalytic reduction of CO2
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A hybrid for the visible-light-driven photocatalytic reduction of CO 2 using methanol as a reducing agent was developed by combining two different types of photocatalysts: a Ru(II) dinuclear complex (RuBLRu′) used for CO2 reduction is adsorbed onto Ag-loaded TaON (Ag/TaON) for methanol oxidation. Isotope experiments clearly showed that this hybrid photocatalyst mainly produced HCOOH (TN = 41 for 9 h irradiation) from CO 2 and HCHO from methanol. Therefore, it converted light energy into chemical energy (ΔG = +83.0 kJ/mol). Photocatalytic reaction proceeds by the stepwise excitation of Ag/TaON and the Ru dinuclear complex on Ag/TaON, similar to the photosynthesis Z-scheme.
- Sekizawa, Keita,Maeda, Kazuhiko,Domen, Kazunari,Koike, Kazuhide,Ishitani, Osamu
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supporting information
p. 4596 - 4599
(2013/05/23)
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- Precision measurement of the quadrupole coupling and chemical shift tensors of the deuterons in α-calcium formate
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Using calcium formate, α-Ca(DCOO)2, as a test sample, we explore how precisely deuteron quadrupole coupling (QC) and chemical shift (CS) tensors Q and σ can currently be measured. The error limits, ±0:09 kHz for the components of Q and ±0:06 ppm for those of σ, are at least three times lower than in any comparable previous experiment. The concept of a new receiver is described. A signal/noise ratio of 100 is realized in single-shot FT spectra. The measurement strategies and a detailed error analysis are presented. The precision of the measurement of Q is limited by the uncertainty of the rotation angles of the sample and that of σ by the uncertainty of the phase correction parameters needed in FT spectroscopy. With a 4-sigma confidence, it is demonstrated for the first time that the unique QC tensor direction of a deuteron attached to a carbon deviates from the bond direction; the deviation found is (1:2±0:3°). Evidence is provided for intermolecular QC contributions. In terms of Q, their size is roughly 4 kHz. The deuteron QC tensors in α-Ca(DCOO)2 (two independent deuteron sites) are remarkable in three respects. For deuterons attached to sp2 carbons, first, the asymmetry factors η and, second, the quadrupole coupling constants CQ, are unusually small, η1 = 0:018; η2 = 0:011, and CQ1 = (151:27±0:06) kHz, CQ2 = (154:09±0:06) kHz. Third, the principal direction associated with the largest negative QC tensor component lies in and not, as usual, perpendicular to the molecular plane. A rationalization is provided for these observations. The CS tensors obtained are in quantitative agreement with the results of an earlier, less precise, line-narrowing multiple-pulse study of α-Ca(HCOO)2. The assignment proposed in that work is confirmed. Finally we argue that a further 10-fold increase of the measurement precision of deuteron QC tensors, and a 2-fold increase of that of CS tensors, should be possible. We indicate the measures that need to be taken.
- Schmitt, Heike,Zimmermann,Koerner,Stumber,Meinel,Haeberlen
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- Evidence for rate limiting C-H bond cleavage in the leuckart reaction
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A rho value of +0.21 is reported for the reaction of mono 4-substi- tuted benzophenones with formamide. This, in conjunction with a kinetic iso- tope effect value of 1.80 obtained for the system, suggests a rate-limiting C-H bond cleavage.
- Awachie, Peter I.,Agwada, Vincent C.
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p. 1899 - 1910
(2007/10/02)
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- METAL-ASSISTED REACTIONS. PART 16. INVESTIGATION OF MECHANISMS OF HETEROGENEOUS LIQUID PHASE CATALYTIC TRANSFER HYDROGENOLYSIS THROUGH DEUTERIUM-LABELLING.
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Hydrogen isotope studies have shown that heterogeneous catalytic transfer hydrogenolysis of C-O bonds in tetrazolyl ethers of phenols (1) in the liquid phase proceeds via direct transfer of hydrogen from an active hydrogen donor centre to the ether on the catalyst surface and not through transfer of hydrogen atoms from the catalyst surface.
- Johnstone, Robert A. W.,Price, Peter J.
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p. 2493 - 2502
(2007/10/02)
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- Mechanism of Photooxidation of Glyoxal and Formaldehyde in Solid O2 at 12-18 K
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The UV photoxidation of solid O2/trans-H2C2O2 samples at 12-18 K gives diformylperoxyl, 2, as the most important primary product (via facile intermediacy of HCO radicals) and *2CO as an important secondary photolysis product.Degradation of these products gives HC(O)OO*CO, HCOOH*COx, H2O2*2CO, H2O*CO2, CO, and CO3.A 30 K warm-up generates H2O2*2CO from 2*2CO by thermal decomposition.The photooxidation of the solid O2/H2C2O2 system is driven less to completion than the photooxidation of the solid O2/H2CO system; because the latter system has more free radical species through the H atom recoil in the H2CO photolysis, the H atoms escape from the photolysis cage and hence a significant change in the photolysis cage stoichiometry occurs.
- Tso, Tai-Ly,Lee, Edward K. C.
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p. 5465 - 5474
(2007/10/02)
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